1. Technical Field of the Invention
The present invention relates to the field of IP facsimile, more particularly to an IP facsimile method for limiting bit rate in IP facsimile. In addition, the present invention also relates to a method for limiting bit rate in IP facsimile by a gateway, which is the key of the technical effect of the method for limiting bit rate in IP facsimile according to the invention, and because it solves certain problems, having technical effect, it is proposed in the same applicant.
2. Background of the Invention
Data is usually transmitted and switched through public switched telephone network (PSTN) in conventional facsimile technique. With the development of data communication and integrated service digital network, more and more facsimiles are transmitted by IP facsimile, i.e., a message transmitter in the PSTN and a message receiver in the PSTN are connected by Internet, and gateways are provided between the transceivers in the PSTN and Internet to modulate and demodulate the data of PSTN and IP data package.
IP facsimile can be classified to real-time IP facsimile and unreal-time one, i.e. IP storage transmission facsimile, IP real-time facsimile. IP storage transmission facsimile means that when the gateway receives the time-division multiplexing data in the PSTN, it stores the data in the transponder but not transmits the data instantly on the Internet after modulation, and when the callee needs receiving the data, such data is transmitted through the gateway. IP real-time facsimile means that when the gateway receives the time-division multiplexing data from PSTN, it transmits the data instantly on the Internet after modulation, it is real-time, which is conventionally used by us.
In the IP facsimile gateway, data are transmitted from PSTN to Internet or from Internet to PSTN, few control function is provided.
Conventional IP real-time facsimile comprises the following steps:
(1) A call connection is set up between the calling fax machine and the called fax machine, the stage is as similar as the process of that of telephone call;
(2) The calling fax machine and the called fax machine handshake, the called fax machine sends a digital identification signal frame, and the highest facsimile bit rate provided by the called fax machine is in the information word of the digital identification signal frame;
(3) The calling fax machine takes out the bit rate from the information word after receiving the digital identification signal frame, then compares the bit rate with the highest bit rate provided by the calling fax machine itself, then takes out the lower and inserts in the digital command signal frame and sends it to the called fax machine, and this bit rate is as the highest bit rate at which message is transmitted;
(4) Transmit the message;
(5) After the message is transmitted, process to the operation of confirmation, error-correction, continuous transmission for many pages;
(6) Release the facsimile call.
It is known from the implementing process of conventional technique, the bit rate of conventional IP facsimile is controlled completely by the calling fax machine and the called fax machine themselves after handshaking, and it can not be controlled by outside apparatus. Once jam happens on the Internet, the network performance will become bad, therefore the higher facsimile bit rate the worse quality of pictures, which may cause unacceptable short line etc. Gateway users hope that when the network becomes bad, gateway can limit the highest bit rate of the facsimile to improve the quality of the pictures and improve the reliability of IP facsimile. This is so-called bit rate limit performance through gateway.